commons-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MATH-1146) class Mean returns incorrect result after processing an Infinity value
Date Sun, 05 Oct 2014 18:40:34 GMT

     [ https://issues.apache.org/jira/browse/MATH-1146?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Phil Steitz updated MATH-1146:
------------------------------
    Fix Version/s: 3.4
         Assignee: Phil Steitz

Will edit javadoc for 3.4 release.

> class Mean returns incorrect result after processing an Infinity value
> ----------------------------------------------------------------------
>
>                 Key: MATH-1146
>                 URL: https://issues.apache.org/jira/browse/MATH-1146
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.3
>            Reporter: david cogen
>            Assignee: Phil Steitz
>             Fix For: 3.4
>
>         Attachments: MATH-1146.patch
>
>
> 1. Create a Mean object.
> 2. call increment() with Double.POSITIVE_INFINITY.
> 3. Call getResult(). Result is INFINITY as expected.
> 4. call increment() with 0.
> 5. Call getResult(). Result is NaN; not INFINITY as expected.
> This is apparently due to the "optimization" for calculating mean described in the javadoc.
Rather than accumulating a sum, it maintains a running mean value using the formula "m = m
+ (new value - m) / (number of observations)", which unlike the "definition way", fails after
an infinity.
> I was using Mean within a SummaryStatistics. Other statistics also seem to be affected;
for example, the standard deviation also incorrectly gives NaN rather than Infinity. I don't
know if that's due to the error in Mean or if the other stats classes have similar bugs.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message